Attempts to increase a calorific value by performing a carbonizing treatment on woody biomass have been made for the purpose of utilizing the energy of woody biomass more efficiently. As the carbonizing treatment for woody biomass, for example, a method in which a pyrolysis furnace such as an external heat type pyrolysis gasification furnace is used, woody biomass is indirectly heated at a high temperature of 300° C. to 700° C. under a low oxygen atmosphere, and thus a carbide with an increased heat amount is produced is known.
As carbide producing methods, high temperature carbonization in which woody biomass is indirectly heated at a high temperature of 500° C. to 700° C. and half carbonization (torrefaction) in which woody biomass is indirectly heated at about 300° C. are known. In the high temperature carbonization, a sufficient treatment time is ensured at a predetermined temperature and thus it is possible to produce a carbide with a high gasification rate and a reduced self-heating property. In the half carbonization, by performing control within a very narrow temperature range, it is possible to produce a carbide in which both crushability and a residual calorific amount are compatible (for example, refer to Patent Literature 1).